Sleep-disordered breathing (SDB) is a common and serious cause of cardiovascular and neurocognitive morbidity in children and adults. Overnight polysomnography is presently the gold standard for the clinical diagnosis of certain forms of obstructed breathing, but such procedures are costly, cumbersome and not readily available. Recently, there has been increasing recognition that heart rate variability analysis using nonlinear dynamics theory may provide a useful, noninvasive marker for the obstructive sleep apnea syndrome (OSAS). This exploratory (R21) project will examine the feasibility and potential advantages of heartrate chaos as a novel measure of the changes in cardiac autonomic tone in adults and children with OSAS. Under the guidelines of the NHLBI Innovative Research Grant Program (PA-03-015), a three-way consortium between Massachusetts Institute of Technology, Brigham and Women's Hospital, and Children's Hospital in Boston has been established in order to provide the necessary bioinformatics/clinical expertise and related clinical databases for systematic evaluation of heart rate variability in OSAS using state-of-the-art analytical techniques. The results will define the nonlinear dynamics of heart rate variability in OSAS as a basis for future development of a reliable and noninvasive ambulatory screening test for OSAS in children and adults. [unreadable] [unreadable]